一個名詞(或其它形式)對另一個名詞或代詞進行修飾，限定或說明，這個名詞(或其它形式)就是同位語。當同位語部分是一個完整的句子時，它就是一個同位語從句。作為具有補充說明和進一步解釋功能的成分及名詞性從句之一，同位語及同位語從句在託福閱讀中出現的頻率是相當之高的。由於同位語及同位語從句表示與之同位的名詞的實際內容，因此它通常會大幅增加句子長度，致使部分考生在閱讀過程中出現句意理解困難的問題。因此，在平時的備考過程中，考生們應當注意將其作為一種長難句結構進行專門的練習。
一、同位語
同位語與被它限定的詞的格式一致，通常緊挨在一起，有時也會出現間隔現象。
1)In the seventeenth century the organ, the clavichord, and the harpsichord became the chief instruments of the keyboard group, a supremacy they maintained until the piano supplanted them at the end of the eighteenth century.
在此句中，the organ, the clavichord, and the harpsichord became the chief instruments of the keyboard group與a supremacy呈現同位語關係：
17世紀時風琴、敲絃琴和撥絃琴成為鍵盤樂器類的主要成員，這種至高無上的地位一直由它們保持，直到18世紀末被鋼琴所取代。
二、同位語從句
同位語從句是個完整的句子，它一般跟在某些名詞後面，用以說明該名詞表示的具體內容。
2)Satire jars us out of complacence into a pleasantly shocked realization that many of the values we unquestioningly accept are false.
在此句中，many of the values we unquestioningly accept are false 為同位語從句，它由that引導，解釋了前面的名詞realization：
諷刺作品使我們擺脫了自滿情緒，並在愉快與震驚之中認識到：許多我們毫無疑問地接受的價值觀是錯誤的。
注意：一般的“抽象”名詞都可以在之後跟同位語從句，例如：reminder(提醒)， realization(瞭解)，skepticism(懷疑)，argument(爭論)，rumor(謠言)，prospect(預期)，evidence(證據)，boast that(引以為豪的事)， claim (宣稱)，words(訊息)等：
3)There are numerous unsubstantiated reports that natural vitamins are superior to synthetic ones, that fertilized eggs are nutritionally superior to unfertilized eggs, that untreated grains are better than fumigated grains and the like.
在此句中，natural vitamins are superior to synthetic ones, fertilized eggs are nutritionally superior to unfertilized eggs, untreated grains are better than fumigated grains and the like 三個同位語從句均由that引導，補充說明前面的名詞reports。
關於天然維生素優於人造維生素，受精蛋比未受精蛋的營養價值更高，未經燻蒸消毒處理的穀物比經過處理的好等等報道屢見不鮮，但都沒有得到證實。
4)It has lived because readers appreciate a refreshing stimulus, an irreverent reminder that they lived in a world of platitudinous thinking, cheap moralizing, and foolish philosophy.
在此句中，a refreshing stimulus與an irreverent reminder呈現同位語關係，而they lived in a world of platitudinous thinking, cheap moralizing, and foolish philosophy亦為同位語從句，由that引導，補充說明了前面的名字reminder：
它之所以存在，是因為讀者欣賞它使人耳目一新的刺激，它毫不客氣地提醒：他們活在一個充滿陳腐思想、廉價的道德說教與荒謬哲學的世界裡。
練習：
a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore.
argument that humans，even in prehistoric times，had some number sense，at least to the extent of recognizing the concepts of more and less when some objects were added to or taken away from a small group, seems fair, for studies have shown that some animals possess such a sense.
3. Keen observers and quick learners, crows are astute about the intentions of other creatures, including researchers, and adept at avoiding them.